How to test high voltage diodes

[stivep1]

I marked this "liked" thank you very much

[RimstarOrg]

@stivep1 Thanks! And you're very welcome.

[lmasisi]

I agree with you with regards to a short, i said that because of the rectification ability of a diode and the fact that once it is in correct operation it has approximately zero resistance. This brings me back to same point, should not the volt drop across the diode be 0.7Volts (this value depends on characteristics of the diode, it could be more or less). I still do not understand why when the diode is connected in the correct polarity the voltage across it is so high???

[RimstarOrg]

@lmasisi It has low resistance in one direction only. The 0.7volts value is the voltage you have to apply across the diode before it will conduct large amounts of current. Once the current starts conducting, the voltage across the diode increases as the current increases.

[lmasisi]

My theory tells me that once the diode is forward biased, then it acts as a short, which means the voltmeter should only read the volt drop across the diode which is normally 0.7 volts. How come this is not so in your video? are you using some special diodes or something ?

[RimstarOrg]

@lmasisi But it's not like a short. A short allows current to flow in both directions. A diode allows current to flow in only one direction. See the diagram at the start of the video again. You are not just measuring across the diode but also across the power supply. The diode allows electrons to flow from one side of the power supply to the other, pumping up the voltage. Measuring a short is like putting both meter probes at the same point in the circuit. I just did that and got 0V as expected.

[PsalmHymn]

Dear Rimmer, I didn't have my eye glasses on and thought this vt. was how to test your high voltage dildoes. . I'd always wanted to have mine tested, but never knew that I could get it checked. . Typical, there isn't any such test for a dildoe, that the one I have could be tested to see if it was still functioning at high voltage, was just a fantasy of mine. . Cheers. from, del-boy.

[RimstarOrg]

@hec031 I don't think so. I sure wouldn't want anyone to damage anything as a result. The test circuit is one I got from the web, and I've used the very diodes I'm marking in the video for Cockcroft-Walton voltage multipliers boards and I've gotten the expected results as shown on my oscilloscope and on my multimeter through high votlage probes. i.e. Boards wired for positive output show as positive w.r.t ground on the scope/meter and negative boards show as negative.

[fakkyouhomo]

hey, i have here one of those small glassy zener diodes . when i test the diode 8 ohms flows in both dirrection. is this one bad ?

[fakkyouhomo]

i have here a diode and i get a reading of 170.(red lead to the enna and black lead to the cetta)  is this diode bad ? its from a philips tft monitor.

[RimstarOrg]

@fakkyouhomo You'll have to give me more information. You get 170 what? Volts? Ohms? What scale is your meter set to? What are you using as a power supply and at what voltage? What do "enna" and "cetta" mean? The terms sound familiar but I can't find any translation for them.

[fakkyouhomo]

@RimstarOrg im sorry but i ment 170 Ohms. its a diode off a printboards from a philips tft . with anne and cetta i mean the red lead goes to the enna and the black to the cetta >| where the white marker is on the black diode... so enna on the diode is where the current goest tru the cetta and not backwards. or els it would be a bad diode. but i just wanted to know if 170 ohms is normal... sorry im strill a noob :(

[RimstarOrg]

@fakkyouhomo I don't know what the resistance should be for your diode, sorry. I'm assuming you're using an analog meter and when you measure in one direction you get nothing (open) and when you read in the other direction you get 170ohms. If so, that sounds good to me. It also doesn't sound like it's a high voltage diode otherwise your meter wouldn't give you any resistance. The voltage that a meter uses for checking resistance is too low for high voltage diodes.

[fakkyouhomo]

@RimstarOrg i also called an expert today. and i asked if its normal that i get no measurement in ohms range from a 0.33 ohm resistor. and they said thats right. most multimieters cant measure that low.. ohwell i thought i say it here...

[djholmes2001]

LOL! you kept on almost saying divide instead of diode in your video. sorry dude i just thought it was funny! i am simple guy you know!!

more videos!!!!!! plz : )

too many people are relying on your hard efforts Steve!

[RimstarOrg]

So I did, LOL! I also say "bee-atch of diodes" at one point. You can probably guess I didn't redub the voiceover afterwards. :-)

As for more videos... I have a number of them partially cone but it's always a tough choice... publish or keep experimenting. You can guess which one wins most often. I'll make more of an effort.

[djholmes2001]

funny and smart your other half must be very happy!!

[djholmes2001]

wassup Steve? it diode dude not divide!!!! lol. experiments looking good!! catch you in the forum. good work as usual!

[RimstarOrg]

Thanks DJ! I'm not sure what you mean by "not divide". Note that these are "high voltage" diodes. The usual simple testing resistance in both directions and the diode settings on some meters don't work. That's why this circuit is used.